This invention relates generally to a process for preparing a value-added recycled polyethylene terephthalate (RPET) polymer blend component. More particularly, the invention is directed to a process for combining post-consumer polyethylene terephthalate and a specialty additive, to produce a polymer blend component that is useful and desirable for the manufacture of new products.
Post-consumer processing of recycled PET to manufacture a variety of low-tech consumer products such as flower pots and fence posts is well-known. Typically, the recycling process utilizes used PET containers, such as discarded carbonated beverage containers, which are collected, sorted, washed, and separated from contaminants to yield a relatively clean source of RPET. Additionally, the manufacture of imperfect and damaged molded PET products, particularly the blow molded bottles used for containing consumer goods, results in a considerable amount of PET waste which the manufacturers of such products would like to reuse. The RPET produced by conventional recycling processes is generally in ground or flake form, which is thereafter melt processed or further pelletized by the end user.
RPET is generally subjected to a grinding operation in order to make the material easier to handle and process. Conventional grinding equipment reduces the RPET to about xe2x85x9c inch particles or flakes. The grinding is conducted in a manner to insure that a consistent flake size will be produced, by employing a grate or screen through which the ground material must pass upon exiting the grinder. Although conventional RPET flakes melt processing and pelletizing equipment is designed to handle xe2x85x9c inch flakes, some RPET materials having sizes as large as xc2xd inch and as small as xc2xc inch are also commercially produced. The bulk density of xe2x85x9c inch flake RPET generally ranges from about 22 to about 35 pounds per cubic foot.
Similarly, RPET and PET pellets are generally formed to a standard, uniform size of about 0.12 inch in diameter. The bulk density of such pellets generally ranges from about 50 to about 58 pounds per cubic foot. Typically, PET and RPET melt processing equipment is designed to accept pellets having the above-mentioned dimensions and physical characteristics.
Regrettably, RPET flakes are difficult to process when combined with specialty additives and other polymeric materials. For example, RPET flakes and specialty additives do not easily result in a homogeneous material when mechanically mixed together, and thus are incompatible with virgin plastic particles in subsequent melting and forming processes.
It would be desirable to prepare an RPET polymer blend component, comprising RPET and a specialty additive, which blend component is beneficial and easily processed when combined with other polymeric materials in subsequent melting and forming operations.
Accordant with the present invention, a process for preparing an RPET polymer blend component, including an RPET carrier and a specialty additive, has surprisingly been discovered. The process comprises providing a quantity of RPET flakes, comminuting the RPET flakes to prepare RPET particles having an average mean particle size from about 500 microns to about 5 microns, adding a specialty additive to the RPET particles, and mixing the RPET particles and specialty additive, to prepare a homogeneous blend of RPET carrier and specialty additive.
The inventive process is particularly useful for preparing a value-added RPET polymer blend component, comprising a specialty additive and an RPET carrier, which may thereafter be blended with additional polymeric materials for the melt processing and forming of, for example, plastic containers.